Sleep Homeostatic and Waking Behavioral Phenotypes inEgr3-Deficient Mice Associated with Serotonin Receptor 5-HT2 Deficits

Abstract

Study Objective: The expression of the immediate early gene early growth response 3 (Egr3) is a functional marker of brain activity including responses to novelty, sustained wakefulness, and sleep. We examined the role of this gene in regulating wakefulness and sleep. Methods: Electroencephalogram/electromyogram (EEG/EMG) were recorded in Egr3-/-and wild-type (WT) mice during 24 h baseline, 6 h sleep disruption and 6 h recovery. Serotonergic signaling was assessed with 6 h EEG/EMG recordings after injections of nonselective 5-HT2 antagonist (clozapine), selective 5-HT2 antagonists (5-HT2A; MDL100907 and 5-HT2BC; SB206553) and a cocktail of both selective antagonists, administered in a randomized order to each animal. Results: Egr3-/-mice did not exhibit abnormalities in the timing of wakefulness and slow wave sleep (SWS); however, EEG dynamics in SWS (suppressed 1-3 Hz power) and in quiet wakefulness (elevated 3-8 Hz and 15-35 Hz power) differed in comparison to WT-mice. Egr3-/-mice showed an exaggerated response to sleep disruption as measured by active wakefulness, but with a blunted increase in homeostatic sleep drive (elevated 1-4 Hz power) relative to WT-mice. Egr3-/-mice exhibit greatly reduced sedative effects of clozapine at the electroencephalographic level. In addition, clozapine induced a previously undescribed dissociated state (low amplitude, low frequency EEG and a stable, low muscle tone) lasting up to 2 h in WT-mice. Egr3-/-mice did not exhibit this phenomenon. Selective 5-HT2A antagonist, alone or in combination with selective 5-HT2BC antagonist, caused EEG slowing coincident with behavioral quiescence in WT-mice but not in Egr3-/-mice. Conclusion: Egr3 has an essential role in regulating cortical arousal, wakefulness, and sleep, presumably by its regulation of 5-HT2 receptors.

State-Dependent Modulation of Visual Evoked Potentials in a Rodent Genetic Model of Electroencephalographic Instability

“…The line of Egr3 −/− mice used in the current work were generated (Tourtellotte and Milbrandt, 1998 ), behaviorally phenotyped (Gallitano-Mendel et al, 2007 ), and polysomnographically phenotyped (Grønli et al, 2016a ) in previous publications. Detailed characterization of breeding and genotyping of the colony at Washington State University is reported elsewhere (Grønli et al, 2016a ). All animals were housed in a 12 h light/12 h dark cycle, (except during VEP measurement; see Experimental protocol: visual evoked potentials ) with food and water available ad libitum .…”

“…Significant sex differences in the phenotypes described in the current study were not detected and are not further considered. Data on sleep timing and the vigilance state-specific EEG characteristics are reported in Grønli et al ( 2016a ).…”

“…EEG state stability and VEP measurements were conducted separately within EMG-defined AW, IW, and QW, as both the EEG manifestation of accumulated sleep need in wild type mice (Grønli et al, 2016b ), and the previously-reported EEG phenotype of Egr3 −/− mice (Grønli et al, 2016a ), are detected only during QW and absent in AW.…”

“…Mice deficient for Egr3 (Egr3 −/− ) show normal sleep timing and duration, with the exception of a modest reduction in REMS. However, during QW, Egr3 −/− mice exhibit elevated electroencephalographic (EEG) synchrony in the 3–8 Hz range and 15–35 Hz (beta) range relative to Egr3 +/+ mice (Grønli et al, 2016a ). This elevated synchrony during QW may indicate reduced sensory processing capabilities in the absence of a functioning Egr3 locus.…”

Nitrogen narcosis induced by repetitive hyperbaric nitrogen oxygen mixture exposure impairs long-term cognitive function in newborn mice

“…In brief, a total of sixteen adult mice were anesthetized with isoflurane, and then two bipolar stainless steel electrodes were planted into the forehead (2 mm after bregma, 2 mm lateral from the midline, and 1 mm deep under the skull) and the ground electrode was attached to prefrontal skin as described by JP, Wisor [ 12 ]. The surgery was performed on a heating pad.…”